1. Field of the Invention
The present invention relates to a liquid crystal dispensing system. More particularly, present invention relates to a liquid crystal dispensing system incorporating gravimeter to facilitate detecting an amount of liquid crystal material being dispensed.
2. Discussion of the Related Art
As various portable electric devices such as mobile phones, personal digital assistant (PDA), note book computers, etc., continue to be developed, various types of flat panel display devices such as liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum fluorescent displays (VFDs), having a compact construction, light weight, and low power-consumption characteristics also continue to be developed. Owing to the ease with which they are driven, and to their superior ability to display images, LCDs are extensively used.
FIG. 1 illustrates a cross sectional view of a related art LCD device.
Referring to FIG. 1, a related art LCD device 1 generally comprises a lower substrate 5, an upper substrate 3, and a liquid crystal layer 7 formed therebetween. The lower substrate 5 (i.e., a driving device array substrate) includes a plurality of pixels (not shown), and a driving device (e.g., a thin film transistor (TFT)) and pixel electrode formed at each pixel. The upper substrate 3 (i.e., a color filter substrate) includes a color filter layer for realizing color and a common electrode. An alignment layer is formed on both the lower and upper substrates 5 and 3 to align liquid crystal molecules of the liquid crystal layer 7. The lower substrate 5 and the upper substrate 3 are attached to each other by a sealant material 9, formed at peripheral regions thereof. Accordingly, the liquid crystal layer 7 is confined within an area defined by the sealant material 9.
Light transmittance characteristics of the pixels are controlled by causing the driving devices to generate electric fields between the pixel electrodes and the common electrode. The generated electric fields reorient liquid crystal molecules of the liquid crystal layer 7 to display a picture.
FIG. 2 illustrates a flow chart of a related art method of fabricating the LCD device shown in FIG. 1.
Referring to FIG. 2, the related art method of fabricating the LCD device described above generally consists of three sub-processes: a TFT array substrate forming process; a color filter substrate forming process; and a cell forming process.
At step S101, a TFT array substrate forming process is performed whereby a plurality of gate lines and data lines are formed on the lower substrate 5 (e.g., a glass substrate) to define an array of pixel areas. TFTs are connected to the gate and the data lines within each pixel area and pixel electrodes are connected to the thin film transistors to drive a subsequently provided liquid crystal layer in accordance with a signal applied through the thin film transistor.
At step S104, a color filter process is performed whereby R, G, and B color filter layers, for realizing predetermined colors, and a common electrode are formed on the upper substrate 3 (i.e., a glass substrate).
At steps S102 and S105, alignment layers are formed over the entire surface of both the lower substrate 5 and upper substrate 3, respectively. Subsequently, the alignment layers are rubbed to induce predetermined surface anchoring characteristics (i.e., a pretilt angle and alignment direction) within the liquid crystal molecules of the liquid crystal layer 7.
At step S103, spacers are dispersed onto the lower substrate 5. At step S106, sealant material 9 is printed at peripheral regions of the upper substrate 3. At step S107, the lower and upper substrates 5 and 3 are pressed and bonded together (i.e., assembled) and the spacers dispersed at step S103 ensure that a cell gap formed between the assembled lower and upper substrates 5 and 3 is uniform.
At step S108, the assembled upper and lower substrates 5 and 3 are cut into unit LCD panels. Specifically, the lower substrate 5 and the upper substrate 3 each include a plurality of unit panel areas, within each of which individual TFT array and color filter substrates are formed.
At step S109, liquid crystal material is injected into the cell gap of each of the unit LCD panels through a liquid crystal injection hole defined within the sealant material. After each cell gap is completely filled with liquid crystal material, the liquid crystal injection hole is sealed. At step S110, the filled and sealed unit LCD panels are then tested.
FIG. 3 illustrates a related art liquid crystal injection system for fabricating the related art LCD device.
Referring to FIG. 3, a container 12, containing a supply of liquid crystal material 14, is placed into a vacuum chamber 10 that is connected to a vacuum pump (not shown). Subsequently, a unit LCD panel 1, formed as described above with respect to FIG. 2, is arranged over the container 12 using a unit panel handling device (not shown). Next, the vacuum pump is operated to reduce the pressure within the vacuum chamber 10 to a predetermined vacuum state. The unit panel handling device then lowers the unit LCD panel 1 such that the liquid crystal injection hole 16 contacts a surface of the supply of liquid crystal material 14. After contact is established, liquid crystal material 14 contained within the container 12 can be drawn through the liquid crystal injection hole 16 and into the cell gap of the unit LCD panel 1 due to a capillary effect. The injection method described above, therefore, is generally known as a dipping injection method.
After contact is established, the rate at which the liquid crystal material 14 is drawn into to the cell gap of the unit LCD panel 1 can be increased by pumping nitrogen gas (N2) into the vacuum chamber 10, thereby increasing the pressure within the vacuum chamber 10. As the pressure within the vacuum chamber 10 increases, a pressure differential is created between within the cell gap of the unit LCD panel 1 and the interior of the vacuum chamber 10. Accordingly, more liquid crystal material 14 contained by the container 12 can be injected into the cell gap of the unit LCD panel 1 and at an increased injection rate. As mentioned above, once the liquid crystal material 14 completely fills the cell gap of the unit panel 1, the injection hole 16 is sealed by a sealant and the injected liquid crystal material 14 is sealed within the unit LCD panel 1. The injection method described above, therefore, is generally known as a vacuum injection method.
Despite their usefulness, the aforementioned dipping and vacuum injection method methods can be problematic for several reasons.
First, the total amount of time required to completely fill the cell gap of the unit LCD panel 1 with liquid crystal material 14, according to the dipping/vacuum injection methods, can be relatively long. Specifically, a cell gap thickness of the unit LCD panel 1 is only a few micrometers wide. Therefore, only a small amount of liquid crystal material 14 can be injected into the unit panel 1 per unit time. For example, it can take about 8 hours to completely inject liquid crystal material 14 into the cell gap of a 15-inch unit LCD panel, thereby reducing the efficiency with which LCD devices can be fabricated.
Second, the aforementioned dipping/vacuum injection methods require an excessively large amount of liquid crystal material 14 compared to the relatively small amount of liquid crystal material 14 actually injected into the unit LCD panel 1. Because liquid crystal material 14 contained by the container 12 is exposed to the atmosphere, or certain other process gases during loading and unloading of the unit LCD panel 1 into and out of the vacuum chamber 10, liquid crystal material 14 contained by the container 12 can easily become contaminated. Therefore, the uninjected liquid crystal material 14 must be discarded, thereby reducing the efficiency with which expensive liquid crystal material is used and increasing the cost of fabricating a unit LCD panel 1.